Thank You Joust

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#1 PUD

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Posted 24 January 2012 - 10:07 PM

Joust pointed out the bootstrap circuit on these older amps.

The C1 Cap  250 v 10 uf  was bad bad bad.

it leaked a Loooong time ago and then just dried out.
when testing it looked ok.

BUT when voltage is applied the breakdown will then show up.

The 10vdc zener had to show a drop of 10vdc from the rail voltage when testing from 87 vdc to 77 vdc.
there was no drop at all.

Bad Cap!

What made me finally think of what was going on I looked at the schematic for the bootstrap and the service bulletins point at the High voltage
being present on the board.

C1 Cap

I had 2 of these amps with the same thing that I got from a sound man at the same time
for real cheap..........
Replaced the other one with the same exact problem  C1 cap and now have 2 amps that work just fine.

That was the problem!

Testing caps "in circuit"  is tough to read and pulling every cap is not very practical.

Thanks again  Joust


#2 joust


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Posted 13 April 2012 - 11:25 AM

You're so welcome!